FIELD OF THE INVENTION
[0001] The present invention relates, in general, to image intensifier tubes and, more specifically,
to an electron gain device, such as a microchannel plate (MCP), configured for close
contact to an electron sensing device, such as a CMOS imager.
BACKGROUND OF THE INVENTION
[0002] Image intensifying devices can use solid state sensors, such as CMOS or CCD devices.
Image intensifier devices amplify low intensity light or convert non-visible light
into regularly viewable images. Image intensifier devices are particularly useful
for providing images from infra-red light and have many industrial and military applications.
For example, image intensifier tubes may be used for enhancing the night vision of
aviators, for photographing astronomical events and for providing night vision to
sufferers of night blindness.
[0003] There are three types of image intensifying devices: image intensifier tubes for
cameras, solid state CMOS (complementary metal oxide semiconductor) and CCD (charge
coupled device) sensors, and hybrid EBCCD/CMOS (electronic bombarded CCD or CMOS)
sensors.
[0004] Referring to FIG. 1, there is shown a schematic diagram of an image intensifier tube,
generally designated as 10. As shown, light energy 14 reflected from object 12 impinges
upon photocathode 16. Photocathode 16 receives the incident energy on input surface
16a and outputs the energy, as emitted electrons, on output surface 16b. The output
electrons, designated as 20, from photocathode 16, are provided as an input to an
electron gain device, such as MCP 18. The MCP includes input surface 18a and output
surface 18b. As electrons bombard input surface 18a, secondary electrons are generated
within micro-channels 22 of MCP 18. The MCP generates several hundred electrons for
each electron entering input surface 18a.
[0005] Although not shown, it will be understood that MCP 18 is subjected to a difference
in voltage potential between input surface 18a and output surface 18b, typically over
a thousand volts. This potential difference enables electron multiplication. Electrons
24, outputted from MCP 18, impinge upon solid state electron sensing device 26. Electron
sensing device 26 may be a CMOS imager, for example, and includes input surface 26a
and output surface 26b, as shown in FIG. 1. Electron sensing device 26 may be fabricated
as an integrated circuit, using CMOS processes.
[0006] In general, the CMOS imager employs electron sensing elements. Input surface 26a
includes an active receive area sensitive to the received electrons from MCP 18. The
output signals of the electron sensing elements may be provided, at output surface
26b, as signals whose magnitudes are proportional to the amount of electrons received
by the electron sensing elements. The number of electrons is proportional to incoming
photons at the cathode. CMOS imagers use less power and have lower fabrication cost
compared to imagers made by CCD processes.
[0007] The output of CMOS imager 26 produces an intensified image signal that may be sent,
by way of a bus, to image display device 28. The output of CMOS imager 26 may be,
alternatively, stored in a memory device (not shown).
[0008] To facilitate the multiplication of electrons between the input of the image intensifier
tube, at input surface 16a, and the output of the image intensifier tube, at output
surface 26b, a vacuum housing is provided. As shown, photocathode 16, MCP 18 (or other
electron gain device) and CMOS imager 26 (or other electron sensing device) are packaged
in vacuum housing 29. In addition to providing a vacuum housing, input surface 26a
of the CMOS imager and output surface 18b of the MCP are required to physically be
very closely spaced from each other.
[0009] Such close spacing presents a problem, because a conventional silicon die of a CMOS
imager, for example, includes wires looping above the input surface of the imager
for outputting the intensified image signal. Because these wires flare out from the
silicon die and loop above the input surface, before they are connected to bond pads
on a ceramic carrier holding the silicon die, it is difficult to closely space the
input surface of the imager to the output surface of the MCP.
[0010] As an example, a conventional silicon die is shown in FIGS. 2a and 2b. As shown,
chip 30 includes silicon die 32 attached to ceramic carrier 34. The silicon die includes
an array of terminal pads 36 for providing input/output (I/O) signals. Hundreds of
terminal pads 36 are typically disposed around the peripheral circumference of silicon
die 32. Also shown in FIGS. 2a and 2b is an array of pads 38 disposed on ceramic carrier
34. Leads or wires 40 are attached by ultrasonic bonding of wires between I/O pads
36 and I/O pads 38, thereby making electrical contact between them. Extending from
the bottom of ceramic carrier 34 are a plurality of pins 42, as shown in FIG. 2b,
which are connected through via-holes (not shown) to the array of bond pads 38. In
this manner, electrical contacts are made between bond pads 36 on silicon die 32 and
the input/output of the chip, at the plurality of pins 42.
[0011] In a typical conventional configuration, wires 40 loop above the planar top surface
of silicon die 32 and then descend down toward ceramic carrier 34, as shown in FIG.
2b. These wire loops above silicon die 32, in the case of a conventional CMOS imager
(for example), prevent a tight vertical placement between the top active surface area
of silicon die 32 and the output surface area of electron gain device 18. As best
shown in FIG. 2c, output surface 18b of electron gain device 18 is placed in close
vertical proximity to the input surface area of silicon die 32. However, because of
the looping of wires 40, it is not possible to reduce the vertical space between output
surface 18b and the top surface of silicon die 32. The lowest wire bond profile is
limited to the wire bond height plus a vertical clearance to assure the wires do not
contact the silicon surface and become shorted. The vertical clearance is also limited
to the bondwire loop height plus a distance required to provide a voltage standoff
between the output surface of the electron gain device and the input surface of the
electron sensing device.
[0012] The present invention addresses this shortcoming by providing an electron gain device
having rectangularly shaped slots, which allow for a tight interface and clearance
between the electron sensing device and the electron gain device (for example an MCP).
SUMMARY OF THE INVENTION
[0013] To meet this and other needs, and in view of its purposes, the present invention
provides a microchannel plate (MCP) for an image intensifier including an active portion
having an input surface area for receiving electrons and an output surface area for
outputting multiplied electrons. The input and output surface areas are oriented horizontally
with respect to each other and spaced by a vertical distance. A non-active portion
surrounds the active portion, where the non-active portion includes at least one slot
extending vertically into the non-active portion and extending horizontally to form
a horizontal slotted area. When the MCP is positioned vertically above an electron
sensing device having wires looping vertically above the electron sensing device,
the slot is configured to receive a portion of the wires, resulting in a vertical
clearance between the MCP and the electron sensing device. The wires loop a vertical
looping distance above a surface of the electron sensing device, and a portion of
the vertical looping distance is configured to be received within the slot. The horizontal
slotted area is a rectangle, and the input and output surface areas are rectangles.
The non-active portion may include two slots, and the two slots form two horizontal
slotted areas, one on one side of the output surface area and the other on the other
side of the output surface area.
[0014] Another embodiment of the present invention includes a method for making an MCP for
an image intensifier. The method includes the steps of: forming an active area by
stacking fiber optic channels having acid etchable core rods and acid resistant cladding
glass surrounding the etchable core rods; and forming a non-active area. The non-active
area is formed by (a) stacking fiber optic channels having acid resistant core rods
and acid resistant cladding glass surrounding the resistant core rods in a first region,
and (b) stacking fiber optic channels having acid etchable core rods and acid etchable
cladding glass surrounding the etchable core rods in a second region. Also included
is a step of etching the active area and the non-active area to form (a) micro-channels
in the active area for multiplying electrons, and (b) at least one slot in the second
region. The one slot is configured to be placed above bondwires of an electron sensing
device to receive the bondwires and provide a close spacing between the MCP and the
electron sensing device.
[0015] Preferably etching the non-active area includes forming two slots in the second region,
and the two slots are configured to be placed above the bondwires of the electron
sensing device to receive the bondwires and provide a close spacing between the active
area of the MCP and the electron sensing device.
[0016] Preferably forming the active area includes stacking the fiber optic channels having
acid etchable core rods and acid resistant cladding glass surrounding the etchable
core rods into a first rectangular shape. Forming the non-active area includes stacking
the fiber optic channels having acid etchable core rods and acid etchable cladding
glass surrounding the etchable core rods into two second rectangular shapes. Etching
the active area includes forming a rectangular active area for multiplying electrons.
Etching the non-active area includes forming two rectangular slots, one on one side
of the rectangular active area and one on the other side of the rectangular active
area.
[0017] Yet another embodiment of the present invention is an image intensifier including
a ceramic substrate, an electron sensing device disposed vertically above the ceramic
substrate, and bondwires looping between the ceramic substrate and the electron sensing
device, where the bondwires loop vertically above the electron sensing device. An
MCP is positioned vertically above the electron sensing device. The MCP includes at
least one slot disposed at an output side of the MCP and vertically above the bondwires
for nestling the bondwires and providing a close separation between the electron sensing
device and the MCP. The MCP may include two slots. One slot nestles the bondwires
on one side of the electron sensing device and another slot nestles the bondwires
on another side of the electron sensing device.
BRIEF DESCRIPTION OF THE FIGURES
[0018] The invention may be understood from the following detailed description when read
in connection with the following figures:
- FIG. 1
- is a schematic illustration of a typical image intensifier tube, including an electron
gain device and an electron sensing device.
- FIG. 2a
- is a top view of an electron sensing device formed in a conventional manner, showing
a ceramic header and bondwires.
- FIG. 2b
- is a sectional view of the electron sensing device shown in FIG. 2a.
- FIG. 2c
- is a sectional view of a conventional electron sensing device, spaced in vertical
proximity to and below an electron gain device, when integrated together in an image
intensifier tube.
- FIG. 3a
- is a sectional view of an electron sensing device spaced below and in close vertical
proximity to an electron gain device, in accordance with an embodiment of the invention.
- FIG. 3b
- is a top view of the electron gain device shown in FIG. 3a, in accordance with an
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Referring now to FIGS. 3a and 3b, there is shown an exemplary image intensifier,
generally designated as 50. Image intensifier 50 includes an electron gain device,
designated as 52, for example a microchannel plate (MCP). Image intensifier 50 also
includes an electron sensing device, designated as 56, disposed on top of ceramic
substrate 60. Electron sensing device 56 may include, for example, a solid state CMOS
(complimentary metal oxide semiconductor) sensor, a CCD (charge couple device) sensor,
or a hybrid electron bombarded CCD or CMOS sensor.
[0020] As shown, electron gain device 52 is disposed above electron sensing device 56. The
electron gain device includes an active region, generally designated as 62 ( also
referred to as a rectangular active area (RAA 62)). It will be appreciated that the
top surface of active region 62 includes an active receiving area sensitive to received
electrons from a photocathode (shown as 16 in FIG. 1), the latter disposed vertically
above electron gain device 52. Electron gain device 52 receives incident energy on
its input surface and outputs amplified energy, as emitted electrons, on its output
surface. The output electrons are provided as an input to electron sensing device
56. For example, electron gain device 52, such as an MCP, generates several hundred
electrons for each electron entering at the input surface.
[0021] As shown, active region 62 is disposed vertically above electron sensing device 56.
The electron sensing device receives the output electrons from electron gain device
52 and provides an output signal that is proportional to the amount of electrons received
by the electron sensing device. Electron sensing device 56 includes wires 58 looping
above the planar top surface of electron sensing device 56 and then descending down
to ceramic substrate 60 for bonding.
[0022] In accordance with an embodiment of the present invention, electron gain device 52
includes slots on opposing vertical sides of active region 62, the slots generally
designated as 54. Each slot is configured to receive a portion of wires 58 with a
gap of 2-6 mils (50-150 microns) in width. As shown, slots 54 provide clearances for
wires 58 at the sides of active region 62. It will be appreciated, of course, that
if an electron sensing device includes looping wires on one side of the device only,
then the slot on the opposing side of the electron gain device may be omitted.
[0023] Since the slots are configured to receive the wire loops above the planar top surface
of electron sensing device 56, electron gain device 52 may be brought into close proximity
to the electron sensing device. Since slots 54 provide additional clearance for bond
wires 58, a smaller distance between electron gain device 52 and electron sensing
device 56 may be realized. The smaller separation distance results in performance
benefits.
[0024] As an example, without slots 54 providing clearances for the wire loops, then a minimum
separation distance of 0,127mm (0.005 inches) is required between the electron gain
device and the electron sensing device. With the slots included for providing clearances
for the wire loops, however, a minimum separation distance of approximately 0,05mm
(0.002 inches) may be realized.
[0025] It will be appreciated that a minimum distance may be maintained between bond wires
58 and the walls of slots 54 of electron gain device 52. This minimum distance may
be determined by the voltage standoff needed to hold off any high voltages that are
applied between the electron gain device and bond wires 58.
[0026] Although FIG. 3a depicts clearance slots 54 as spanning vertically from the input
side to the output side of electron gain device 52, nevertheless, the vertical clearance
is only required with respect to the bottom side of electron gain device 52 and the
looping wires of electron sensing device 62. Thus, the clearance slots need not span
the entire distance between the input output surfaces of electron gain device 52.
[0027] In another embodiment of the present invention, it may be desirable to provide physical
contact between the output surface of the electron gain device and the input surface
of the electron sensing device. In this embodiment, the gap width of clearance slots
54 may be such that the loops of bond wires 58 may be received entirely within the
clearance slots. If direct physical contact between the electron gain device and the
electron sensing device is made, such direct physical contact may mitigate any vibration
concerns due to the electron sensing device bracing the electron gain device.
[0028] Referring next to FIG. 4, there is shown method 70 for forming clearance slots in
an MCP (for example), the method designated generally as 70. As shown, step 71 forms
fibers of glass core surrounded by glass cladding. The glass core is made of material
that is etchable, so that the core may be subsequently removed by etching. The glass
cladding is made of glass that is non-etchable under the same conditions that allow
etching of the core. Thus, each cladding remains after the etching process, and the
cladding material becomes a boundary for each micro-channel that forms upon removal
of a corresponding core. A suitable cladding glass is a lead-type glass, such as corning
glass 8161.
[0029] As described in
U.S. Patent 7,126,263, issued on October 24, 2006, which is incorporated herein by reference in its entirety, the optical fibers are
formed in a draw machine which incorporates a zone furnace. The temperature of the
furnace is elevated to the softening temperature of the glass. The fiber is fed into
a traction mechanism, where the speed is adjusted until a desired fiber diameter is
achieved. These individual fibers are then cut into shorter lengths of approximately
18 inches.
[0030] Method 70 then enters step 72 and forms multiple hexagonal arrays of fibers, each
referred to as a bundle or a multi-assembly. A bundle is formed from several thousands
of the cut links of single fibers, which are stacked into a mold and heated at the
softening temperature of the glass, where each of the cut lengths has a hexagonal
configuration.
[0031] The bundle is again suspended in a draw machine and drawn to again decrease the fiber
diameter, while still maintaining the hexagonal configuration of the individual fibers.
The bundle is then cut into shorter lengths of approximately 6 inches. Several hundred
of the cut bundles are then stacked, in step 73, to form individual rectangular cross-sectional
areas (for example), where each cross-sectional area defines a rectangular active
area (RAA). One RAA, for example, is shown in FIG. 3b designated as 62.
[0032] Next, method 70 enters step 74 to stack completely etchable glass (also referred
to as rods) on opposing sides of the RAA. As an example, the stacked etchable glass
forms the rectangular regions which later will form the clearance slots designated
as 54 in FIG. 3b.
[0033] Next, step 75 stacks non-etchable glass to surround both the stacked etchable glass
and RAA region 62. The non-etchable glass forms region 51 of electron gain device
52 in FIG. 3b. Accordingly, RAA region 62 forms the active area of MCP 52, regions
54 form the clearance slots on opposing sides of RAA region 62, and region 51 forms
the non-active portion of the MCP.
[0034] Step 76 presses the stacks into a monolithic stack. Next, step 77 dices the monolithic
stack into multiple MCPs.
[0035] During a standard etching process, the etchable multi fibers are completely etched
away leaving open slots to accommodate the looping wires. The etchable glass cores
in the RAA region form the micro-channels. The non-etchable glass surrounding the
clearance slots and the RAA region forms the non-active area of the MCP and provides
support for mounting the MCP within the image intensifier tube.
[0036] The present invention may be used for any application that requires a close proximity
between two devices, where physical clearance between the two devices is an issue.
The physical clearance issue does not necessarily have to result from bond wires looping
above a top surface of a device, but may result from any physical body protruding
above another body.
[0037] Another application for the present invention may be in using the slotted apertures
for venting purposes during processing of the MCP. Presently in film-less MCP based
image intensifier tubes, vent holes are drilled into the metal tube body components
to provide venting of gases during processing. The clearance slots of the present
invention may eliminate any need for vent holes in the metal tube body, if the vents
are located within the MCP itself.
[0038] Although the invention is illustrated and described herein with reference to specific
embodiments, the invention is not intended to be limited to the details shown. Rather,
various modifications may be made in the details within the scope and range of equivalents
of the claims and without departing from the invention.
1. A microchannel plate (MCP) (52) for an image intensifier (50) comprising an active
portion (62) having an input surface area for receiving electrons and an output surface
area for outputting multiplied electrons, the input and output surface areas oriented
horizontally with respect to each other and spaced by a vertical distance, and a non-active
portion surrounding the active portion, the non-active portion including at least
one slot (54) extending vertically into the non-active portion and extending horizontally
to form a horizontal slotted area,
wherein when the MCP is positioned vertically above an electron sensing device (56)
having wires (58) looping vertically above the electron sensing device, the slot (54)
is configured to receive a portion of the wires, resulting in a vertical clearance
between the MCP and the electron sensing device.
2. The MCP (52) of claim 1 wherein the wires (58) loop a vertical looping distance above
a surface of the electron sensing device, and at least a portion of the vertical looping
distance is configured to be received within the slot.
3. The MCP (52) of claim 1 or 2 wherein the MCP (52) is positioned vertically above the
electron sensing device (56), resulting in the vertical clearance of an amount equal
to or greater than a remaining portion of the vertical looping distance.
4. The MCP (52) of claim 1 or 2 wherein the MCP (52) is positioned vertically above the
electron sensing device (56), resulting in the vertical clearance of an amount substantially
close to zero.
5. The MCP (52) of claim 3 or 4 wherein the vertical clearance is approximately 0,05mm
(0.002 inches).
6. The MCP (52) of claim 1 wherein the slot (54) extends vertically into the non-active
portion by an amount between 2-6 mils (50 and 150 microns).
7. The MCP (52) of claim 1 wherein the horizontal slotted area is a rectangle, and the
input and output surface areas are rectangles.
8. The MCP (52) of claim 7 wherein the non-active portion includes two slots, and the
two slots form two horizontal slotted areas, one on one side of the output surface
area and the other on the other side of the output surface area.
9. The MCP (52) of claim 1 wherein the electron sensing device (56) is disposed vertically
above a ceramic substrate (60), and the wires (58) loop between the electron sensing
device (56) and the ceramic substrate (60) , and two slots (54) are configured to
receive the wires looping vertically above the electron sensing device (56).
10. The MCP (52) of claim 1 wherein the active portion (62) includes stacked fiber optic
channels having acid etchable core rods and acid resistant cladding glass surrounding
the core rods, and the non-active portion includes stacked acid etchable fiber optic
channels having acid etchable core rods and acid etchable cladding glass surrounding
the core rods, and the slot (54) is formed by etching away the acid etchable fiber
optic channels.
11. A method for making an MCP (52) for an image intensifier, the method comprising the
steps of:
forming an active area (62) by stacking fiber optic channels having acid etchable
core rods and acid resistant cladding glass surrounding the etchable core rods ;
forming a non-active area by
(a) stacking fiber optic channels having acid resistant core rods and acid resistant
cladding glass surrounding the resistant core rods in a first region, and
(b) stacking fiber optic channels having acid etchable core rods and acid etchable
cladding glass surrounding the etchable core rods in a second region; and
etching the active area and the non-active area to form
(a) micro-channels in the active area for multiplying electrons, and
(b) at least one slot in the second region;
wherein the at least one slot is configured to be placed above bondwires of an electron
sensing device to receive the bondwires and provide a close spacing between the MCP
and the electron sensing device.
12. The method of claim 11 wherein etching the non-active area includes forming two slots
(54) in the second region, and the two slots are configured to be placed above the
bondwires of the electron sensing device (56) to receive the bondwires and provide
a close spacing between the active area of the MCP (52) and the electron sensing device.
13. The method of claim 12 including the steps of:
placing the MCP (52) above the electron sensing device (56);
aligning the two slots (54) with respective sides of the electron sensing device including
the bondwires; and
providing a small clearance between the electron sensing device and the active area
of the MCP.
14. The method of claim 11 wherein forming the active area includes stacking the fiber
optic channels having acid etchable core rods and acid resistant cladding glass surrounding
the etchable core rods into a first rectangular shape, forming the non-active area
includes stacking the fiber optic channels having acid etchable core rods and acid
etchable cladding glass surrounding the etchable core rods into two second rectangular
shapes, etching the active area includes forming a rectangular active area for multiplying
electrons, and etching the non-active area includes forming two rectangular slots,
one on one side of the rectangular active area and one on the other side of the rectangular
active area.
15. An image intensifier (50) comprising a ceramic substrate (60), an electron sensing
device (56) disposed vertically above the ceramic substrate, bondwires (58) looping
between the ceramic substrate (60) and the electron sensing device (56), the bondwires
looping vertically above the electron sensing device, and an MCP (52) positioned vertically
above the electron sensing device (56),
wherein the MCP (52) includes at least one slot (54) disposed at an output side of
the MCP and vertically above the bondwires (58) for nestling the bondwires and providing
a close separation between the electron sensing device and the MCP(52).
16. The image intensifier of claim 15 wherein the slot (54) is formed from bundled fiber
optic channels, including glass material that is completely etchable.